1. Field of the Invention
The present invention relates to an optical information recording/reproducing device wherein information is simultaneously reproduced by irradiating an optical beam to a plurality of tracks, and an optical information recording/reproducing method.
2. Related Art Statement
Optical recording media such as optical cards include a plurality of tracks arranged in parallel. An optical information recording/reproducing device includes an optical head for optically recording/reproducing information to/from an optical card and performs an information recording/reproducing operation by reciprocating an optical recording medium in the direction of tracks of the optical recording medium and reciprocating an optical head perpendicularly to the direction of the tracks.
Generally, as a conventional optical information recording/reproducing device, a single track reading type information recording/reproducing device which irradiates a single light emitted from an optical head onto a single track and reads out information per track has been known. However, such a device cannot increase its reproducing rate because the reproducing rate of information recorded on a track is determined by the relative velocity between the optical head and the optical recording medium.
In order to solve such a problem, an optical information recording/reproducing device of the type which irradiates light emitted from an optical head onto a plurality of tracks and simultaneously read out information from the plurality of tracks has been considered. For example, Japanese Laid-open Patent Publication No. 2-141932 discloses a device which samples binary signals from light receiving elements arranged on a plurality of tracks at high-frequency clocks, stores the signals in a memory, and performs a signal processing, thus realizing a small-sized data processing system.
In an optical card, the recording pit on a track has a length of 2 .mu.m and less. Generally, 1-pit has a length of about 2 fm after modulation. Since the data recording track has a length of about 60 mm, one track can record data of about 30 kbit(=60 mm/2 fm) after modulation. The above prior art discloses that suppressing jitter due to a sampling error to less than 5% results in no adverse effect on data reproduction. If the reciprocating rate is about 640 mm/sec, the passing time per bit is 3.125 .mu. sec.
In consideration of the above facts, in order to suppress the jitter to about 5%, if the binary signals are sampled at a periodic sampling clock of about 156 (3.125 .mu. sec.times.20) nsec, a memory with about 600 kbit (30 kbit.times.20) per track is needed. Such a large capacity memory is usually used as a DRAM memory. Since the access time is about 100 nsec, which is slower than that of a SRAM, the cycle time is about 150 nsec.
In the above device which reads sampled binary signals in a memory and executes a demodulation process track by track, the memory reading time of 150 nsec per bit equals to the data reading time of an optical card.
Hence, for example, in the three-track simultaneous reading device, if the rate of the reciprocating motion is about 640 mm/sec, the total data demodulation time of three tracks takes triple as much as 93.8 msec (60 mm/640 mm/sec). The three-track simultaneous reading device is effective in the case of a slower reciprocating rate and is effective when high-speed memory will be available at lower price in the future.
However, there is a disadvantage in that it is difficult to realize a plurality of tracks reading type optical information reproducing device with a high data reading speed when the relative moving rate between an optical head and an optical card is relatively high, and the existing large capacity, high speed memories are expensive.
Since the conventional optical information recording/ reproducing device performs what is known as a blank check when a track to be recorded is scanned prior to recording information on an optical medium and it is judged whether the track is readable (blank) or not, normal information writing probability is improved.
However, in the single light source-type optical information recording/reproducing device where recording and reproducing corresponds to varying the intensity of a single beam, the recording operation and the reproducing operation cannot be performed simultaneously and in parallel. For that reason, when a normal information recording is performed on one track, at least two scanning operations are needed for blank checking and information recording. Therefore, there is a problem in that it is difficult to increase an effective recording speed at high speed when a continuous recording operation is performed on a plurality of adjacent tracks or tracks connected to each other.